Not applicable
1. Technical Field
This invention relates to laser beam processing of electronic circuits and, in particular, to a system and method employing a laser beam and substrate positioning system having coarse, intermediate, and fine positioning stages for positioning a workpiece and a laser beam relative to each other.
2. Background of the Invention
Lasers have long been employed for various ablating, drilling, and micro-machining applications, such as etched-circuit board (xe2x80x9cECBxe2x80x9d) via drilling, integrated circuit (xe2x80x9cICxe2x80x9d) fusible link ablating, circuit element trimming, and micro-machining of silicon, piezo-electric, and ceramic circuit elements. In each of these electronic circuit processing applications, a positioner system is employed to position a workpiece and a laser beam relative to each other. For example, ECB via drilling typically requires long positioning moves of moderate precision, whereas IC fusible link ablating requires short positioning moves of high precision. Accordingly, different positioner architectures are typically employed for each application.
Traditional positioning systems are characterized by X-Y translation tables in which the workpiece is secured to an upper stage that moves along a first axis and is supported by a lower stage that moves along a second axis that is perpendicular to the first axis. Such systems typically move the workpiece relative to tool, such as a fixed laser beam position or laser spot and are commonly referred to as stacked stage positioning systems because the lower stage supports the inertial mass of the upper stage which supports the workpiece. Stacked stage positioning systems are, however, relatively slow because the starting, stopping, and change of direction of the inertial mass of the stages increase the time required for the laser tool to process all the target locations on the workpiece.
In split-axis positioning systems, the upper stage is not supported by, and moves independently from the lower stage. The workpiece is carried on a first axis or stage while the tool, such as a reflecting mirror and associated laser beam focusing lens, is carried on the second axis or stage. Split-axis positioning systems are advantageous as the overall size and weight of the workpiece increases, utilizing longer and hence more massive stages. Split axis systems are frequently employed in micro-machining and ECB via drilling applications.
More recently, planar positioning systems have been employed in which the workpiece is carried on a single stage that is movable by two or more actuators while the tool remains in a substantially fixed position. These systems translate the workpiece in two dimensions by coordinating the efforts of the actuators. Some planar positioning systems may also be capable of rotating the workpiece.
FIG. 1 shows a conventional way of providing two-axis deflection of a laser beam by employing a high-speed short-movement positioner (xe2x80x9cfast positionerxe2x80x9d) 60, such as a pair of galvanometer driven mirrors 64 and 66. FIG. 1 is a simplified depiction of a galvanometer-driven X-axis mirror 64 and a galvanometer-driven Y-axis mirror 66 positioned along an optical path 70 between a fixed mirror 72 and focusing optics 78. Each galvanometer-driven mirror deflects the laser beam along a single axis to direct the beam to the target location on a workpiece 79. U.S. Pat. No. 4,532,402 of Overbeck discloses a stacked stage beam positioning system that employs such a fast positioner, and U.S. Pat. Nos. 5,751,585 and 5,847,960 of Cutler et al. disclose split-axis beam positioning systems in which the upper stage(s) carry at least one fast positioner. Systems employing such fast positioners are used for nonlink blowing processes, such as via drilling, because they cannot currently deliver the beam as accurately as xe2x80x9cfixedxe2x80x9d laser head positioners.
The split-axis nature of such positioners may introduce rotational Abbe errors, and the galvanometers may introduce additional positioning errors. In addition, because there must be separation between the two galvanometer-controlled mirrors, the mirrors cannot both be located near the entrance pupil to the focusing optics. This separation results in an offset of the beam that can degrade the quality of the focused spot. Moreover, two-mirror configurations constrain the entrance pupil to be displaced farther from the focusing optics, resulting in an increased complexity and limited numerical aperture of the focusing optics, therefore limiting the smallest achievable spot size.
What is still needed, therefore, is a system and method for achieving higher electronic circuit processing throughput while maintaining positioning speed, distance, and accuracy along with focused spot quality consistent with the particular processing application.
An object of the invention is, therefore, to provide a system and method for achieving higher electronic circuit laser processing throughput.
Another object of the invention is to provide a positioner system employing linear, galvanometer, and two-axis steering mirror stages that coact to optimize positioning accuracy, speed, and laser spot size for a variety of electronic workpiece processing applications.
Yet another object of the invention is to provide a positioner system employing coordinated motion for electronic circuit laser-based processing applications.
A preferred embodiment of a tertiary positioner system of this invention employs a combination of processing elements, such as a computer, microprocessor, and digital signal processor (hereafter singly or collectively xe2x80x9cDSPxe2x80x9d) to control a laser beam deflection stage, an X-axis translation stage, and a Y-axis translation stage to direct a laser beam to target locations on a workpiece, such as an IC or ECB. Although the tertiary positioner system is configured with a single laser beam deflection stage mounted on the X-axis translation stage and a single workpiece mounted on the Y-axis translation stage, other configurations of positioning systems, such as ones in which multiple laser beam deflection stages are employed in combination with stacked, split, or planar positioners.
A system control computer processes a tool path database stored in a database storage subsystem. The database contains the desired processing parameters for cutting holes or profiles with the laser beam in the workpiece. The system control computer conveys laser control portions of the stored database to a laser controller and position control portions as a data stream to a profiling process that resolves the data stream into position, velocity, and time components for each intended change in the path of the laser beam across the workpiece.
The laser controller is controlled by timing data generated by the profiling process and further coordinated by a triggering process that synchronizes the firing of a laser to the motion of the laser beam deflection stage and the X- and Y-axis translation stages.
The positioning commands are received by a low-pass filter having a constant signal propagation delay L and by a delay L element that compensates for the propagation delay. The low-pass filter conveys low-pass filtered position command data through an adder to a low-frequency controller, which drives the X and Y-axis translation stages. Delay L element conveys the unfiltered positioning commands from the position profiler to signal processing elements for driving the laser beam deflection stage.
The X- and Y-axis translation stages include position sensors, which convey an actual position of the translation stages to an adder that subtracts the actual position from the low-pass filtered command data to close the control loop and direct the translation stages to the commanded position.
Another adder subtracts the actual position from the delayed positioning commands and produces a low-frequency stage position error signal that is conveyed to a mid-pass filter and a delay M element. Mid-pass filtered position error data is passed through an adder to a mid-frequency controller, which drives galvonometer-deflected mirrors in the laser beam deflection stage. Because midpass filter 109 produces filtered position error data having a constant time delay M, the constant time delay M is compensated for by delay M element, which delays conveying the low-frequency error data to the signal processing elements for driving the laser beam deflection stage.
The galvonometer-deflected mirrors include position sensors, which convey an actual position of the galvonometer mirrors to an adder that subtracts the actual position from the mid-pass filtered error data to close the control loop and direct the galvonometer driven mirrors to the commanded position.
Yet another adder subtracts the actual galvonometer position signal from the delayed error signal produced and produces a high-frequency stage position error signal that is conveyed to a high-frequency controller, which drives a high frequency stage in the laser beam deflection stage.
This invention substantially reduces the effects of low- and mid-frequency stage settling times by adding an FSM within the laser beam deflection stage.
The tertiary positioner system employing the FSM increases electronic circuit processing throughput by decreasing the time required to move the laser beam between target locations and by decreasing the processing time at each location. Adding the FSM as a third positioning stage provides more accurate positioning because positional and settling time errors caused by the first two stages can be corrected by the FSM.
In an alternative embodiment, the FSM may be positioned to receive the laser beam from the galvanometer-driven X- and Y-axis mirrors and deflect it through focusing optics toward the workpiece.